1. Field of the Invention
The invention relates to a power supply system and control method for the system, more particularly, relates to the charging circuit for a battery connected to a load that changes in characteristics, such as the length of service life, brightness, etc., if a voltage exceeding a rated voltage is applied thereto, and control method for the charging circuit.
2. Description of the Related Art
It has been proposed that a battery for a vehicle be installed in a trunk room instead of an engine room. Installation of a battery in a trunk room makes it possible to dispose the battery apart from the engine. However, the trunk is apt to be affected by external temperature. That is, if the external temperature decreases, the battery temperature also decreases. Therefore, a measure for temperature changes is needed. In general, it is effective to change the charging voltage of a battery in accordance with the temperature of the battery.
Japanese Patent Application Laid-Open No. HEI 4-351436 describes an art for changing the charging voltage of a battery in accordance with the temperature of the battery. More specifically, as the battery temperature becomes lower, a higher charging voltage is set to charge the battery.
However, care must be taken if among loads connected to a battery to be charged, there is a load, for example, a bulb or the like, which changes in characteristics, such as the length of service life, brightness, etc. if receiving an applied voltage higher than its rated voltage. That is, if the battery temperature is low, a high charging voltage is needed, so that a charging voltage exceeding the rated voltage of the load is applied to the load in some cases. As a result, the characteristics of the load connected to the battery deteriorate although the battery is efficiently charged.